U-235 exists only in trace amounts among the much more common U-238; they are chemically identical and cannot be separated through any simple process.
Then one needs a perfect gun barrel, a perfectly machined uranium slug and uranium target, and heavy shielding to prevent the process and the device from being spotted by purpose-built detectors including satellites in space. Any minor flaw can be magnified by orders of magnitude and degrade performance. It cannot be easily tested until it is actually used (the Manhattan Project scientists decided to simply use the Little Boy on Japan and focused instead on testing the far more complex plutonium weapon in the Trinity test).
Once completed, a uranium gun device weighs nearly as much as a heavy artillery piece, which means that once one has it, it cannot be easily transported, much less delivered to an enemy country. The Iranians don't have a rocket that big, and won't for decades. I'm not sure the United States has a rocket that big, any longer.
The Iranians, if they wished to use such a device on the Israelis, would have to drag the weapon through or over at least two other hostile countries just to reach Israel, leaving the only practical option as hiding the device in a ship and sneaking it into an Israeli port in times of relative peace, which is probably also not easy.
A sneak attack with a single nuclear weapon would provoke an overwhelming response from other nuclear powers in addition to Israel, too. Nor would a single U-235 bomb do enough damage to materially prevent retaliation from the Israelis. It would guarantee the deaths of millions of Iranians, the total destruction of their modern infrastructure, the death and dissolution of their government, and the complete loss of control of the Persian Gulf and the vast majority of their oil reserves.
More sophisticated nuclear devices present similar technical and logistical problems for the Iranians, even if they are easier to deliver.
So, one can easily conclude, the Iranians don't want nuclear weapons for offensive purposes. They want a nuclear weapon so that they can plaster any invasion fleet or armored columns that would dare to try to steal their oil. Their best bet might be to place the weapons deep underground, over their own oil fields, so that if someone tries to take them, nobody can easily use the facilities or the oil itself.
That, I think, is the big lie behind Israel's position. Whatever crap they're spewing about Iran's capabilities, the real intent is not to protect Israel, but to keep Iran unprotected from a future attempt to steal their Persian Gulf oil fields. And that's also exactly why Iran wants The Bomb.
I personally don't think they can be stopped, just like the Pakistanis and North Koreans could not be stopped, and in both of those prior cases, once those nations got the bomb, their territorial and border problems (with India and South Korea, respectively) suddenly diminished considerably. So it might not be the worst thing in the world... for a while.
= new reply since forum marked as read
